FIG. 1 is an illustration of selected components of a disk drive 10 according to the prior art. The disk drive includes at least one magnetic recording disk 12 that rotates on spindle 13 in direction 15 driven by a spindle motor (not shown). Housing or baseplate 16 provides support for the components. The upper portion of the outer protective case, which is present for normal operation, is removed for this illustration. The data is recorded in concentric or spiral data tracks 26 that are generally circular. Only a small sample of the many tracks are shown. In practice there are thousands of tracks that extend 360 degrees around the disk. The disk drive includes actuator 14 that pivots on pivot point 17 driven by a rotary voice coil motor (VCM) (not shown). The actuator 14 includes a rigid actuator arm 18. A flexible wiring cable 24, which is usually called the “flex cable,” connects the devices on the actuator including read and write heads (not shown) in the slider 22 and the read/write integrated circuit chip (R/W IC) 21 shown) to the drive's system electronics (not shown). The R/W IC 21, which is interchangeably called the arm electronics chip or preamplifier chip, is typically mounted on the actuator arm as shown or integrated into the flex cable. A suspension 20, which is attached to the end of arm 18, includes a flexure/gimbal element (not shown) on which the air-bearing slider 22 is mounted to allow flexible movement during operation. As the disk 12 rotates, the slider with read/write heads is selectively positioned over a track to read and write the magnetic transitions. Disk drives often have more than one disk mounted on the spindle and the upper and lower surfaces of each disk can have magnetic recording material thereon, and the actuators with components mounted thereon are replicated as needed to access each of the recording surfaces.
The flex cable 24 provides electrical connections between the actuators and the system electronics on a circuit board (not shown). The flex cable 24 is rigidly attached by stationary bracket 23 at one end, which connects to the system electronics. The other end of the flex cable is attached to the set of actuators 14 which move in unison in response to the VCM.
A plurality of electrical paths (not shown) extend from the flex cable along the actuators to the arm electronics chip 21. The arm electronics chip is in turn connected by a plurality of electrical paths that extend through the suspension 20 and connect to the slider 22 as further illustrated in FIG. 2A. These electrical paths are typically called traces 31 and are made of copper. The load beam structure of the suspension is a spring metal layer, which is typically stainless steel. The tail end of the suspension has a set of tail termination pads 33 for electrical connection to the corresponding traces 31. The traces carry the signals for the readers (read heads), writer (write head) in the slider, as well as any additional signals required for fly height control by heater protrusion actuation, etc. The example suspension in FIG. 2A has eight termination pads that provide connection to eight slider connection pads 35 that are in turn connected to the slider (not shown) at the slider (or head) end 20H of the suspension. Differing numbers of pads and corresponding traces are common. The traces can vary in width and additional structures/features can be included in the paths to control electrical parameters such as impedance. Dielectric material separates the traces from the spring metal layer and a covering layer dielectric material is typically deposited over the traces. Subtractive and/or additive photolithography, deposition and etching processes can be used to manufacture suspensions and form the traces.
Typically the stainless steel spring metal layer in the suspension has been used as a ground plane for the traces. Because of the spatial constraints imposed on the suspension a multi-layer or stacked trace configurations have been used. Klaassen, et al. in U.S. Pat. No. 6,608,736 disclose stacked read signal traces arranged on top of each other and separated from each other by a dielectric layer and separated from the stainless steel base layer by another dielectric layer.
U.S. Pat. No. 8,094,413 to Hentges, et al. (Jan. 10, 2012) describes a disk drive head/slider suspension flexure with stacked traces having differing configurations on the gimbal and beam regions. A head suspension is described that includes integrated lead suspension flexure having stacked traces that run along one side of the spring metal layer and multi-layer traces that run along the other side. The traces come together in the tail region of the suspension where the set termination pads provide electrical connection to the system. The head suspension component includes stacked traces having first and second traces in the first and second conductor layers, respectively. The stacked traces are used for the writer in an embodiment and the multilayer traces are used for the reader and fly height traces and include a ground layer.
U.S. Pat. No. 8,233,240 to Contreras, et al. Jul. 31, 2012 describes an integrated lead suspension (ILS) in a magnetic recording disk drive has the transmission line portion of the ILS between the flex cable termination pads at the tail and the gimbal area formed of multiple interconnected segments, each with its own characteristic impedance. At the interface between any two segments there is a change in the widths and in impedance of the electrically conductive traces of the transmission line. The number of segments and their characteristic impedance values are selected to produce the largest frequency bandwidth with a substantially flat group delay from the write driver to the write head.
FIG. 2B illustrates a reader MR sensor, such as a tunneling magnetoresistive (TMR) transducer 22R, that is included in a slider and the preamplifier 21R that is included in arm electronics chip 21. The electrical signals pass through the traces in the suspension 20 described above. The TMR transducer is supplied with a current bias which allow changes in the resistance to be reflected in the signal. The signal can be amplified by current-sensing or voltage-sensing amplifier with a single-ended or differential input signal. The bias generator and the amplifier are typically combined and referred to as the preamp and included in the integrated circuit. The processed amplified signal is then sent to the system electronics through the flex cable either as a single-ended or differential signal.
U.S. Pat. No. 4,706,138 to Jove, et al. (Nov. 10, 1987) describes an transimpedance amplifier is used for biasing and amplifying the signals produced by an TMR transducer or MR (w/o tunnel effect). Electrically, the resistance, Rh, of the TMR sensor is disposed as degenerative feedback in the emitter circuit of a differential pair comprising the input stage of the amplifier. In this circuit configuration, a signal representing ΔRh/Rh is sensed and amplified as a current through the TMR sensor. Bias current for the TMR sensor is supplied by the same constant current source that supplies current to both transistors comprising the input stage of the amplifier. To correct for direct current (DC) offset arising from variations in input stage transistor characteristics and the steady-state value of Rh, DC feedback to the input stage, via a level shift and amplifying stage, balances current flow in both paths of the differential input stage.
As areal densities continue to increase, recording schemes using more than one read transducer (reader) in each slider are being explored since having multiple readers allows higher density recording. FIG. 3 is an illustration of a section view (in parallel with the air-bearing surface) of a selected components of a prior art slider 22 with multiple read transducers/sensors R1 . . . Rx. As shown each read transducer is flanked by a pair of shields S2 and S1. There is significant physical separation between the transducer, which leads to skew in relation to the tracks on the disk.
For Multiple Input Multiple Output (MIMO), also called Two Dimensional Magnetic Recording (TDMR), there are two or more magneto-resistive read transducers. Problem areas in front-end system design for multiple-reader architectures include: 1) slider design; 2) suspension interconnection lines, and 3) multiple reader preamplifier design. Each TMR transducer normally requires two electrical differential lines (wires) from the slider to the preamplifier. There is limited room for these electrical paths between the slider and the preamplifier. Each trace path has a design/engineering cost associated with it.
For the present disclosure, a three-reader (3R) architecture configuration and an independent differential amplifier (IDA) is assumed as the current state of the art. A 3R slider design using IDAs requires six connection pads (R1, −R1, R2, −R2, R3, & −R3) on the surface of the slider, which will consume much of the available external area on the slider and slider pads for electrical connections.
In addition, having three separate independent readers requires additional space between read transducers inside the slider. Having additional distance between read transducers creates skew problems caused by physical distance between the transducers. The fly-height control between transducers also creates spacing control problems due to the additional distance between them. For the suspension interconnection, having six conductive traces creates area issues in the layout, where the suspension's tail width space is limited. For the preamplifier, having IDAs requires additional IC area and power, which are key design constraints for the electronic packaging (flex area and mechanical connection to actuator).
For the above three segments of the front-end system, a design solution is needed to minimize the overall required area, power requirement with low electronic noise.